Method of purifying tetrachloroethylene



Patented May 7, 1935 I e Gerald B. Coleman, manila, Mich.,' assignor toH The Dow Chemical Oomli h ,'Midland, Mich,

a corporation of Michigan 1 No Drawing. Application November 20 1933,

x Serial No; 698,927

comin s; (01. 260-162) 7 of zpurifying tetrachloroethylene.

Commercial tetrachloroethylene usually is contaminated withimpuritieswhichcarinot satis- 5 factorily 'be removed by usualmethoidae. g. 'frac-. tional distillation, and which render, the mate:

This invention concerns. an improved method rial-unsuited to certainpurposes wherein the pure compound is-required'. The composition, ofsuchimpurities is notdefinitely known, but they are 10 believed toconsist largely of chlorinated aliphatic hydrocarbons .otherthan.tetrachloroethylene, organic acid chlorides,phosgene/etcr-Some of'theimpurities are relativelyrunstabletoxic materialswhich r n he: com atraehlo o-r ethylene particularly unsatisfactory for pharma;

' ceuticaluses.

The Lunstable toxic igpu'iities have beentoformwith benzidine a yellowcolor or a floccu lent precipitate, accordingto the amount of suchimpurities present. The presence of such impuri-I ties canreadily bedetected bytreating a sample of tetrachloroethylene, with anapproximately equal:volu ne of a 10 percent solution of b enzidineinbenzene and permitting the resultant so- I lution-to stand in thedarkfor 12 hours. I Ifat the close of this period ayellow color ,or aprecipitate has-developed, the tetrachloroethylene is contaminated; withunstable toxic impurities of the type mentioned above. If noyellow coloror pre-. 39 cipitate has developed, the 'tetrachloroethylene is.practically free of such unstable toxic i1 npurities.

This test will hereinafter be; referred to as the benzidine test;

I have now foundthat technical tetrachloro- 1' 5 ethylene canbe'purified completelyby treating the same with aluminum or an aluminumhalide and thereafter separating the purified product by usualprocedure, e. g. fractional distillation.

The invention, then, consists in the method of 40 purifyingtetrachloroethylene hereinafter fully described and particularly pointedout in the claims, the following description and examples setting forthin detail'only certain of the various ways in which the principle of theinvention may be employed.

Technical tetrachloroethylene istreated with a small quantity, e. g.about 1 per cent its weight or more, of anhydrous aluminum chloride. The

resultant mixture isheatedto a temperature at 50, which hydrogenchloride is liberated and the operation preferably iscontinued untilhydrogen chloride is no longer evolved. After such treatment withaluminum chloride, the mixture can be fractionally distilled to separatesubstantially pure tetrachloroethylene. Prior to distillingpuriemployed, but are not to be construed fied tetrachloroethylene fromthemixture I prefer to destroy or remove the anhydrous aluminum.chloride by. usual procedure, e. g. washing with. mineral acid or water,adding a base and filtering,

etc. :The residual organicmaterial islwashed ally distilled.

Instead of" separating I purified tetrachloroethy' l i NT. OFFICEthmwghlywith w e dried, and then fracltion lene as described above Ifind that the separae tion can be carriedout most satisfactorily and infewest steps by fractionally: steam distilling the mixture which resultsfrom the treatment of chloride. During suchoperation a relatively. smallfraction of low boiling material is first collected followed bythe mainfraction of pure tetrachloroethylene and water. The tetrachloroethylenetechnical tetrachloroethylene with aluminum n water fraction-distillsatapproximately 86-87? q C. at 746'millimeters'pressure; Thevtetrachloroethylene layer of the distillate separated and dried, e. g.over anhydrouscalciumchloride,

sodium sulphate, 'or other dryingiagentr I r In purifying.tetrachloroethylene by the. above I I method, I have found it mosteconomical'and sat isfactory to employ; the al'uminurn chloride; inamountrepresenting about l per centthe weight.

ofnthe;tetrachloroethylene used; Itfwill be understood, however, i thatthe aluminum, chloride may be'used in larger amount, if necessary,,or,'30 tains only tracesof-impurities, a smaller amountof aluminum;chloride may successfully be used; instead of treating technicaltetrachloroethylv whenthe tetrachloroethylene to be purified 1 conenewithaluminum chloride, the impure tetraf chloroethylene may be contactedwith metallic aluminum, preferably atan elevated temperature. ent intetrachloroethylene react with aluminum to form a mixture from whichpuretetrachloro ethylene can readily I have found that impurities usuallypres-r be separated by fractional distillation. v

, The following examples describeseveral ways in' which the principleofmy invention has been ing the invention. i

i Example 1 as limit- Commercial tetrachloroethylene, from stock 7 Vwhich hadfirst-been tested and found to have the specific gravity 1,591and boiling point C. atpatmospheric pressure and to give a stronglypositive benzidine test, was treated with a l per cent its weight ofaluminumchloride. The

mixture was heated under reflux for 2 hours. It

was then cooled, wa'shedwith water, dried, and;

distilled. There was obtained pure tetrachloroethylene of boiling point120.3-120.8 C. at atmospheric pressure and specific gravity 1.621 at 20C. as compared with water at 4 C. The purified tetrachloroethylene gavea negative benzidine test.

Example 2 weight of an aqueous calcium hydroxide-slurry, containing 1.2per cent by weight of calcium hydroxide. The aqueous mixture wasfractionally steam distilled, the fraction boiling at 86-87" C. at 746millimeters pressure being collected. The organic layer of this fractionwas separated and dried over calcium chloride. It was found to besubstantially pure tetrachloroethylene, boiling at 11'7.4'-120.4 C. at746 millimeterspressure and having the specific gravity 1.615 at 20 C.with respect to water at 4 C. The purified tetrachloroethylenewas foundto give anegative benzi-- dine test. 7

Example 3 A mixture of 5 grams of aluminum turnings and 350 grams oftechnical tetrachloroethylene, from stock which had been tested andfound to boil at 117.6l26.1 C.; to have the specific gravity 1.584, andto give a; strongly positive benzi'di-ne test, was heated ,underrefluxfor 3 hours. ,Durv irig said operation, a; portion of the aluminum wasdissolved and considerable hydrogen chloride was evolved. The reactedmixture was steam' dis tilled withoutfractionation and the organic layerofthe distillate was separated. dried. and fractionally distilled toobtain substantially pure tetrachloroethylene. The purifiedtetrachloro'ethylone boiled at 1l 9.6-120.6' C. at atmospheric pres sureand had the specific gravity'lfil'l at 20 C. with respect to water at 4C. I It was found to give a negative benzidine test.

Instead of aluminum chloride, other aluminum halides, e. g. aluminumbromide or aluminum' iodide, may be employed in purifying ormanufacturing tetrachloroethylene as hereinbefore described." However,such other aluminum halides are relatively expensive so that I prefer toemploy aluminum chloride in the process.

Other modes of applying the principle of my invention may be employedinstead of those explained, change being made as regards the methodherein disclosed, provided the step or steps stated by any of thefollowing claims or the equivalent of such stated step or steps beemployed.

Itherefore particularly point out and distinctly claim as my invention:-

1. In a method of purifying tetrachloroethylene'; the steps whichconsist in treating impure tetrachloroethylene with about 1 per cent itsweight of aluminum chloride at above room temperature and thereafterdistilling the mixture to separate purified tetrachloroethylenetherefrom.

2. Ina method of purifying tetrachloroethylw ene, the steps whichconsist in treating impure tetrachloroethylene with a relatively smallportion of a material selected from the class consisting of aluminum andaluminumhalides-"at a temperature at which hydrogen "halide is evolvedand thereafter distilling relatively pure tetrachloroethylene from themixture. I

3. In a method of purifying tetrachloroethyh ene, the steps whichconsist in heating a mixture of impure tetrachloroethyleneand a materialse-- lected from'theclass consisting of aluminum and aluminum chlorideto a temperature at which hydrogen chloride is evolved and thereafterdistilling relatively pure tetrachloroethylene from the mixture. I

4.. In a'method of purifying tetrachlorothyh ene, the steps whichconsist in heating impure tetrachloroethylene with a relatively smallportion of aluminum chloride to a temperature at which hydrogen chlorideis evolved, thereafter,

removing aluminum chloride from the treated mixture, and distilling thelatter to separate relatively pure tetrachloroethylene therefrom.

5. Ina method of purifying tetrachloroethylene, the'steps which consistin heatingimpure tetrachloroethylene with aluminum chloride to atemperature at which hydrogen chloride is evolved and thereaftersteam-distilling relatively pure tetrachloroethylene from the mixture.

6. In a method of purifying tetraehloroethylene, the steps which consistin heating impure tetrachloroethylene with a relatively small portion ofaluminum chloride to a. temperature at which hydrogen chloride isevolved and thereafter fractionally steam-distilling relatively pure tetrachloroethylene from the mixture.

" GERALD H. COLEMAN.

